An existing cellular mobile communication system (such as the third generation, 3G), and the fourth generation (4G) network) is a typical network with infrastructure, and uses multiple low-power transmitters (small coverage areas) in place of a high-power transmitter (large coverage area). Small coverage corresponding to each low-power transmitter is called a cell. A group of channels is allocated to each cell, and each cell uses a group of radio resources. Neighboring cells use different radio resources to prevent interference with each other. Cells that are faraway from each other may use the same radio resources repeatedly, which gives rise to spatial multiplexing of radio channel resources and improves system capacity significantly.
Existing device-to-device (Device-to-device, D2D) communication is a terminal self-organizing communication mode without requiring control exercised by a base station or an access node, which makes the communication or networking very flexible.
A D2D communication system introduced between terminals in the cellular mobile communication system brings a series of benefits, for example, 1) a nearby local service may be implemented through a relay between terminals in D2D communication instead of being implemented by the base station, thereby reducing occupation of base station resources; 2) coverage defects of an existing network can be overcome, and the problem of persistent coverage holes in the coverage area of the existing cellular mobile communication system can be eliminated; 3) power consumption can be reduced, and when communication is implemented by several short paths instead of one long path, the power sum of the several short paths is less than the power required by the one long path; and 4) the introduced self-organizing mode increases the capacity of the entire mobile communication system and increases spatial multiplexing.
Both cellular communication and D2D communication require transmission over limited spectrum resources. In the conventional mode, the spectrum resources required for cellular communication transmission are different from and independent of the spectrum resources required for D2D communication transmission, which avoids interference between the cellular communication transmission and the D2D communication transmission. However, because the cellular communication and the D2D communication occupy different spectrum resources, the spectrum utilization efficiency is reduced.